JPH0775028B2 - Substrate marking method by bar code, substrate marked by the method, and substrate having identification information - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates generally to bar code constructions useful for displaying alphanumeric data. More specifically, the present invention provides that the bars exhibit a uniform single width dimension and a particular periodicity, and are coded to include a subsequence of timing marks to enhance readability, and provide bidirectional readability. For barcodes that include a compact end mark. The present invention is particularly useful as a high density bar code system that can be used in the manufacture and processing of semiconductor wafers used in the manufacture of electronic circuit chips such as those produced in very large scale integrated (VLSI) circuit manufacturing processes. Is. However, the bar code of the present invention can also be used in general process automation applications wherever compact codes and / or robust codes are desired.

[0002]

Bar code fonts for displaying symbol data, especially alphanumeric symbols, are based on optical character recognition (OC).
R) It is highly desirable as it provides a machine-readable mechanism that is system independent. OCR systems are generally more error prone than bar code systems.
However, bar code systems are also sensitive to certain error conditions. One example of this is to partially cover the barcode with an opaque film, or reduce the contrast ratio, which makes it more difficult to distinguish between wide and narrow bars. As an example, if the scanning speed of the bar code reader is not quite constant, then a long space gap between the bars is more likely to cause a read error. Bar codes with multiple blank spaces between bars are particularly prone to this type of error. For example, in one bar code, to generate a read error,
A speed variation of 3% is sufficient. Therefore, it will be appreciated that it would be desirable to be able to construct a bar code system that has a significantly reduced sensitivity to scan velocity variations.

Many bar codes use bars having a plurality of different (adjusted) widths. However, there are disadvantages to multi-width barcode fonts. In particular, its density, e.g. expressed in characters per inch, is not as high as that obtained with fonts displaying only single width bars. Moreover, in bar code systems that use multiple bar widths, the circuit must identify each bar width. Or at least it is necessary to identify the width ratio between the bars. The adjusted bar width also causes writing problems when performing scribing with a pulsed laser for imaging. Wider bars, i.e. bars having a width wider than the laser spot width, reduce the quality of the bar image and require a much longer writing time. For this reason, the laser irradiation density increases, so
Adjusted bar width codes have a high risk of damaging the wafer. Furthermore, when pulsed lasers are used to write in a semiconductor wafer in a dot matrix fashion, they tend to form trenches, causing the laser used to read the transmitted signal to malfunction. Therefore, the adjusted bar width system tends to cause readability problems in the presence of write quality problems, bar image degradation or low contrast, such as occurs in semiconductor wafer serial number identification.

When single width bar codes are used, they need to be used concurrently with another timing mark. Therefore, a single width bar code requires twice the space and double reader. Typical examples of such codes are found in envelopes coded by the United States Postal Service. Dual readers are more expensive, and the codes used occupy more space on the wafer. This space is much more devoted to human readable code versions.

The present invention relates generally to bar code reading systems with wide applicability to process automation, manufacturing, marketing, sorting and identification functions, but is particularly applicable to semiconductor wafer identification. In particular, in the manufacture of very large scale integrated circuit devices, that is, chips manufactured from processed wafers made of materials such as silicon, it is possible to write effectively, and robust code under urgent processing in abnormally harsh environments. It is necessary to use. Such codes are robust and have a full range of alphanumeric characters (AZ and 0-9).
Is required to be satisfied. This set comprises a total of 36 characters. However, the letter "O" is often removed from the required set,
A total of 35 characters remaining are typically needed to be displayed and / or identified. Furthermore, due to the size constraints that exist in the manufacture of semiconductor devices, it is desirable for the codes used to exhibit high density. Therefore, code that requires another set of timing marks is undesirable due to the space required by those timing marks.

Further, code suitable for semiconductor chip processing is generally easy to write on a wafer during processing,
And likewise must be easy to read during wafer or chip processing. Further, the bar code font used must be such that it can withstand the processing conditions, often exposure to harsh chemicals and high temperature environments. Still further, it is desirable to use a code that is writable by a pulsed laser. Such robust and reliable code is desired for wafer fab processes to facilitate automated wafer handling, processing, and identification of process parameters. Yet another desirable option is to have a bar code that can be scanned in both directions, with some mechanism ensuring that the correct symbol interpretation is not affected by backward code reading. Furthermore, it will be appreciated that the codes developed for such a process will have broad applicability in other areas where barcodes are currently used.

[0007]

SUMMARY OF THE INVENTION In accordance with a preferred embodiment of the present invention, a method of bar code marking a substrate includes the step of providing a sequence of uniform width marks at selectively spaced intervals. Each mark possesses substantially the same width, and there is a blank space between the marks. The width of the blank spacing is substantially equal to an integer multiple of the second width that represents the width of a single blank space. More specifically, the present invention provides a concise way to identify directional codes in the sense that the backward scan of the code provides an indication that backward interpretation will result in invalid code symbols. Use end marks. Nevertheless, the method of the present invention uses a single width bar.

Further in accordance with the invention, a sequence of marks is such that it includes subsequences that are separated by a fixed distance from marks of adjacent subsequences. This provides a means for timing recovery and / or timing compensation. According to a particular embodiment of the invention, each character or symbol is represented by a sequence of 12 marks and / or spaces. This allows the display of up to 35 or 36 different symbols, which is sufficient for alphanumeric displays. Further, the present invention preferably uses a bar code in which the marks are spaced to display a number of different symbols such that the maximum distance between bars of adjacent different symbols is minimized. In the preferred embodiment of Applicants' invention, this minimum distance is 5 bars wide. This latter feature of the present invention reduces the occurrence of sequences of symbols that produce wide gaps without bars. In addition, the invention also relates to a substrate marked according to the method described above, including a substrate having such an identification mark thereon.

Accordingly, it is an object of the present invention to provide a high density (eg, in characters per centimeter) bidirectional bar code system.

Another object of the invention is to extend a unidirectional bar code to be readable or scannable in either direction by providing an indication of the proper direction.

Yet another object of the present invention is to provide a high density bar code particularly suitable for use in identifying wafers and / or chips in semiconductor manufacturing processes.

It is a further object of the present invention to invent a robust, reliable, single width, self-clocking bar code.

It is also an object of the present invention to provide a bar code which can be used in harsh environments and which is readily writable on materials commonly used in semiconductor manufacturing, and especially materials such as silicon.

Another object of the present invention is to provide a bar code system which displays a single width bar and further self-clocks.

Yet another object of the present invention is to provide a bar code which exhibits the smallest distance value among all the maximum distances between adjacent bars in a sequence of different symbols.

It is a further object of the present invention to provide a bar code system capable of displaying up to 35 or 36 different symbols, such as 36 alphanumeric symbols (AZ and 0-9).

Finally, but not by way of limitation, it is an object of the present invention to provide an easy to read and write bar code which has universal applicability for making identifications.

The subject matter considered to be the invention is pointed out with particularity in the introductory part of the specification and is explicitly claimed. However, the present invention may be best understood with regard to its structure and method of implementation, as well as further objects and advantages thereof, by referring to the following description in conjunction with the drawings.

[0019]

1 illustrates a preferred embodiment of the present invention.
In particular, FIG. 1 illustrates a presence / absence single width bar code capable of displaying the numbers 0 through 9 and the letters A through Z (except for the letter "O"). Therefore, it can be seen that this code can display 35 distinct symbols.
The flattened U-shaped channel mark on the bottom of each bar code symbol is shown for convenience only to point out the fixed distance occupied by each set of bar code symbols.
Of particular note is that each code symbol character has the same horizontal distance and consists of multiple single-width vertical bars and correspondingly sized spaces between these bars. Is. Further, when combined into an alphanumeric character sequence, it can be seen that the first bar of each code forms part of a bar sequence that can provide timing information. Other features of the bar code shown in FIG. 1 and labeled herein as BC412 are discussed in detail below in comparison to other single width bar codes.

In particular, consider now FIGS. 2 and 3, which illustrate various single width bar codes including the code BC412 described above. 2 and 3 show the presence of a bar in the code in the form of the letter "I". The space, or absence of the bar, is indicated by a hyphen "-". Of particular note is the code BC4 shown in FIG.
12 is to always start with an "I-" sequence.
In this case, these two code symbols constitute two sub-sequence elements that are repeated in any chain of bar code symbols. In code BC412, it can be seen that the total number of code elements is 12, so that this code has a fixed length. Moreover, there is always a total of 4 bars per alphanumeric character in these 12 slots (elements) where bars are present or absent. This fact is useful again in establishing or reestablishing timing control. Correspondingly, each symbol contains a total of eight spaces (absence of bars) per letter symbol. Therefore, it can be seen that the code BC412 can display 35 characters. This is sufficient for many alphanumeric applications. Most important to code BC412 is that the maximum number of spaces between bars in any chained sequence of code symbols is five. This means that the blank space runs between adjacent bars are not long. This greatly improves the readability and reliability of such barcodes. There is at least one space between the bars. Therefore, the first and last elements are bars and spaces, respectively.
In particular, in order to control the sensitivity of the reader to speed fluctuations, bar codes with a minimum number of spaces between bars have been found to be preferable. This is because when the reader reads the bar / space sequence, it detects the presence of the bars and derives the number of spaces between the bars from the scan speed and time. If the scan speed is not quite constant, long space gaps between bars are more prone to read errors. As an example of this, the BBC31 code shown in FIG. 3 has a maximum of 17 spaces between bars. Such codes are prone to read errors with only 3% speed variation. However, on the contrary, B
The C412 code has a maximum of 5 spaces between bars, so it is readable even at 8% speed variation. This is a great advantage for the BC412 code.

Another bar code in accordance with the present invention is illustrated by the code labeled BC313 in FIG. It can be seen that the code BC313 also has timing marks specific to the code structure for the same reasons given above for the code BC412. Therefore, codes such as BC412 and BC313 do not require the presence of another set of timing marks. However, code BC313 owns one more element per symbol than code BC412. Nevertheless, it is possible to fully display the alphanumeric character set of 36 different symbols. Code BC313 includes a total of 3 bars per character and a total of 10 spaces per character. Furthermore, the maximum number of spaces between bars is eight, which is greater than the corresponding maximum distance of code BC412. However, both codes BC412 and BC313 display single width barcodes incorporating a timing recovery subsequence. In addition, codes BC412 and B
Each C313 possesses sufficient unique and identifiable structure so that it can be easily extended to code with more than 12 elements per displayed character.

FIG. 3 also illustrates some other single width bar codes, code BC411, code BBC31 and code BC311. It will be appreciated that these are all examples of single width barcodes, but do not possess the desired self-clocking properties. Furthermore, code B
BC31 is in particular missing the range of different symbols that can be displayed, i.e. 31 with respect to code BC412 35 above or code BC313 above 36.
The characteristics of the various codes shown in FIGS. 2 and 3 are listed in Table I below. Table I BC411 BC412 BBC31 BC311 BC313 Number of elements 11 12 10 11 13 Number of bars / character 4 4 1 to 5 3 3 Number of spaces / character 7 8 5 to 9 8 10 Maximum number of spaces between bars 7 5 17 7 8 Timing bar No. Yes No No Yes Number of characters 35 35 31 36 36

Of particular note, of the four codes with a fixed number of bars in Table I, code BC412 has the smallest maximum number of spaces between bars, ie 5 spaces. This is the most strongly desired feature as mentioned above. Also, code like BBC31
It can be seen that it does not even possess the desirable property of having a fixed number of bars or spaces per symbol character displayed.

1 of the BC412 bar code shown in FIG.
In one implementation, the semiconductor wafer identifier consists of seven characters, one of which is the checksum character. The 7-character identifier is encoded into the appropriate bar code sequence according to the BC412 code definition. In addition, a bar is added at the end of the coding sequence. In reading the resulting bar code, the first of the bar / space sequence is
Starting with the 12th, every 12th element is a bar and is recognized as the beginning of a character. The reference notch on the wafer is
Used to accurately determine the direction of the coded bar / space sequence. However, in the absence of the reference notch, this coded sequence may actually be read from the opposite direction and recognized as a valid wafer identifier, which is an error. That is, as shown in FIG. 1, the BC412 code is a unidirectional barcode.

However, this point of the BC412 code can be easily changed by adding spaces and bars instead of just bars as the terminal pattern for the coded character sequence. In this case, if the sequence is read in the reverse direction (the direction indicated by arrow 20), the 13th encountered element is a space. That is, probably all characters except the first are
It's absurd because it starts with a space instead of the required bar. This is illustrated in FIG. A bar code version of the letters "1DIRECT" is shown there. In particular, when this bar code pattern is scanned in the direction of arrow 20, it can be seen that every 12th slot after the first bar contains spaces rather than bars, as indicated by arrow 30. Thus, the end marks including spaces and bars can make the BC412 code readable in both directions at the following points. In particular, the code can be determined from the inversely read bar / space sequence pattern. In this example, it is straightforward to invert the bit pattern representing the code symbols so that the signals are generated in the proper (inverted) sequence. In this way, BC41 with end marks
It can be seen that the two codes can be easily scanned in both directions.

However, even though the BC412 code with the above end mark is scannable in both directions, there are other situations that still occur during the scanning operation, so it is desirable to further modify the BC412 code. . In particular, the barcode may be scanned obliquely during the scanning operation, and the scanning operation may start at the center of the barcode. In this case, the first segment of the barcode element is completely missed. In addition, the oblique scanning of the bar code causes the first segment of the bar code element to be recognized, but the scanning segment to be completely different from the direction perpendicular to the bar, thus causing the bar code end segment to be read at all. It may not be. Other situations besides oblique scanning also result in incomplete data collection. In such a situation, it is desirable to be able to identify not only the end mark of the bar code but also the start indicator. Thus, bar codes with start and stop marks or indicators can avoid problems with oblique scanning, or at least provide an indication that the number of bar code elements scanned is incomplete. Therefore, the start and stop bar code display (in the situation to compensate for it)
It has been found desirable to further modify the BC412 code as provided. Therefore, the main advantages of start and stop bar code indicators are:
Despite the diagonal scan and symbol dropout problems, a variable number of symbols is easily displayed by the barcode.

As further pointed out above, it is also often desirable to have bar codes that possess bidirectionality. However, special start and stop bar code elements increase the length or size of the code. In applications involving marking of semiconductor devices, using more bar code elements than necessary proves to be generally undesirable due to the need to reduce the amount of device real area consumed by the indicia. . Therefore, it is desirable to meet the conflicting goals of being able to provide sufficient bidirectionality and variable length (where desired), although the start and stop marks contain a small number of elements.

Accordingly, Table II is provided below as an optional chart or selection space layout to describe the 13 different variations available as start and stop symbols. As in FIGS. 2 and 3, the letter "I" indicates a bar and the hyphen "-" indicates a space. Table II provides 13 different variations for start symbols and corresponding stop symbols. Table II also shows which of these 13 start and stop symbol sets provide bidirectional and variable length coding for the BC412 code shown in FIGS. Table II also shows the number of additional bar code elements required by including each set of start and stop characters. When introduced into the BC412 coding scheme, there is overhead in space utilization as these are additional barcode elements that are not present in the original barcode. This overhead is shown as a percentage in the rightmost column of Table II. In particular, the percentages shown are based on an increase in the number of barcode elements for the 7-symbol BC412 message set as shown in FIG. However, in the percentage calculation, the last two barcode elements shown in FIG. 4 were actually considered as part of the overhead used to calculate the percentages shown in Table II.

While it is often desirable to have bidirectionality and variable length as features of barcodes, it is likewise desirable to use barcode schemes that exhibit a minimum amount of overhead. Therefore, Option 7 shown in Table II
Can provide the desired features while at the same time having a minimal amount of overhead (ie space or true area of the chip)
Turns out to be the first code listed. Therefore, option 7 is one of the preferred choices for providing bidirectionality and variable length for barcodes constructed in accordance with the present invention. Therefore, the start symbol "I-
I ------ "may be effectively used in conjunction with the BC412 code as part of a scheme to provide bidirectional and variable length features. Further, as a stop or end mark, As in the bar code element sequence "-
I "(readable as a" space bar ") is preferably used. Table II Over Option Start Stop Number of Elements Bidirectional Variable Length Head 1 I 1 No No 1.2% 2 -I 2 Yes No 2.4% 3 I- -II 6 Yes No 7.1% 4 I ------ I 8 Yes No 9.5% 5 I ------ -I 9 No Yes 10.7% 6 I ------ II 10 Yes No 11.9% 7 II ------ -I 11 Yes Yes 13.1% 8 I--I ----- I-- -I 14 Yes Yes 16.7% 9 IIIIIII- -I 16 Yes Yes 19.0% 10 I --- ---- -I 10 Yes Yes 11.9% 11 I -------- -I 11 Yes Yes 13.1% 12 II ------- -I 12 Yes Yes 14.2% 13 I--I- ----- -I 12 Yes Yes 14.3%

Another thing to note is that for the minimum overhead shown, the option 10 bar code has only 11.9% overhead,
It also provides both bidirectional and variable length features. However, having 7 consecutive spaces in a row, this code is somewhat more sensitive to scan speed variations. Thus, it can be seen how difficult it is to simultaneously optimize all criteria of bidirectionality, variable length, and lack of sensitivity to scan speed variations.

To more fully understand the preferred variation choice, consider two cases with two subcases. In the first example, bidirectionality and fixed length are assumed to be the preferred choice (case 1). Option 2 if the start character (set of bar code elements) is not present and "-I" is the end mark
Is preferred because it requires less space. In the second example, bidirectionality and variable length are assumed to be the desired features (case 2). And if space requirements are important (subcase 1), option 10 is preferred. On the other hand, if the purpose is to reduce the scanning speed dependence (subcase 2), it is preferable to use "II ------" as the start character (or mark) and "II" as the end character. Note that this letter selection is not specifically shown in Table II. Table II illustrates that this provides a mechanism for selecting ranges of start and stop characters independently of each other without departing from the design purpose of the BC412 code.

FIG. 4 is also useful for displaying the single width aspect of the code of the present invention throughout. This figure is also useful for explaining the twelve "slots" present in the BC412 code. The figure also shows the simplicity of the end marks. (The hatch marks used in FIG. 4 are an alternative to black-painting the area of the figure and are not for displaying the cross section.)

The system of the present invention is particularly applicable to marking semiconductor materials for identification during processing. The application of single-width character fonts provides higher code density, easier writing and easier reading. This is because the reading system only recognizes the presence or absence of bars and does not need to identify the width of the bars or the width ratio between the bars. When applied to silicon wafers, the bar width is typically between about 0.10 millimeters and 0.05 millimeters. This is because the pre-polishing mark and post-polishing mark writing methods each have a code density of 12 to 6 characters per centimeter. Higher densities are possible by writing with a narrow bar and read by a high resolution reader. In one embodiment of the invention, a bar having a 4 mil (0.1 millimeter) width is used. Such bars are placed with a center-to-center spacing of 10 mils (0.25 mm) with a minimum width between adjacent bars of 6 mils (0.15 mm). With this size, the bar width is 4 mils (0.1 mm) and the space width is 6 mils (0.15 mm).

The marks are preferably written on the semiconductor substrate by an exchangeable Nd: YAG laser operating in dot matrix mode. High quality bars are produced on silicon wafers without overlapping dots.
By etching and chemical and mechanical polishing action,
The mark is further transformed into a continuous line.

As described above, the bar code mark of the present invention is
It is highly desirable to be able to withstand the harsh environment of VLSI processing methods. The temporary process overlay obstructs some of the bar code and / or reduces the contrast ratio, thus complicating the bar code reading situation. Figure 5A
And FIG. 5B clearly shows that the code of the system written in silicon semiconductor material can survive exposure to acidic and alkaline chemicals.

Now consider a system capable of reading such marks located on a substrate such as a wafer. Of particular note, it can be seen from FIG. 6A that the light source and reflection sensor 10 is capable of directing a source of light, preferably laser light, onto the substrate of the wafer 18. The light reflected from the wafer 18 is the functional block 10
Of the sensor to generate an electrical signal as shown in FIG. 6B. This signal is amplified by the amplifier 12 and transmitted to the peak detector 14 and the comparator 16.
Comparator 16 produces the desired binary output, BC412.
Or, display a concatenated string of characters found on the wafer 18 in the form of a barcode such as BC313.

From the above, it should be appreciated that the bar code system of the present invention is entirely capable of fulfilling the purposes set forth herein. In particular, it can be seen that the present invention provides a single width, bidirectional bar code that exhibits unique self-clocking characteristics. Further, it can be seen that this code has a full range of alphanumeric character sets. It will also be seen that this preferred code exhibits a minimum for the maximum number of spaces that occur between bars. It is further noticed that the codes detailed here show unique timing sub-sequences that originate from the leading code bar, but also code that produces a timing mark sub-sequence in either the code center or the trailing sequence. It is possible. Any of these arrangements are possible without departing from the spirit of the invention. Further, while the present invention has been described in detail herein with reference to semiconductor wafer and / or chip processing, the system disclosed herein is broadly applicable to any system that commonly uses bar codes. Should be noted. More specifically, the term "substrate" as used herein, including in the claims, is not limited to semiconductor materials. The substrate may be paper, such as a backside adhesive label, wood, metal, plastic, composite, or other material that is marked or capable of accepting marking indicia on its surface portion. The marking is provided by the ink or by altering the surface properties or other physical properties of the material. It also includes, but is not limited to, electrical and / or magnetic properties. Therefore, "
The term "mark" should not be construed as limited to visible marks.

Although the present invention has been described in detail herein in accordance with certain preferred embodiments thereof, many modifications and variations will occur to those skilled in the art. Accordingly, such modifications and changes are intended to be covered by the appended claims as fall within the true spirit and scope of the invention.

Since the single-width bar code of the present invention is constructed as described above, it can be read in both directions and can have a high density. Therefore, it is particularly useful for use in wafer or chip identification in semiconductor manufacturing processes.

[Brief description of drawings]

FIG. 1 illustrates a preferred bar code system of the present invention.

FIG. 2 is an illustration of two single width barcodes with embedded timing marks according to the present invention.

FIG. 3 is an illustration of three single width barcodes without embedded timing marks.

FIG. 4 is an enlarged illustration of the BC412 barcode shown in FIGS. 1 and 2, and more particularly showing inclusion of an end mark, which is typically found in unidirectional codes. A code with no features is provided.

FIG. 5A is a plan view of a bar code mark on a semiconductor substrate that has been acid etched. FIG. 5B is a plan view similar to FIG. 5A except that the use of alkali etching is described.

FIG. 6A is an illustration of a system capable of reading a code generated in accordance with the present invention. 6B is an illustration of signals generated by the bar code reading system shown in FIG. 6A in accordance with the present invention.

[Explanation of symbols]

10 Light Source and Reflection Sensor 12 Amplifier 14 Peak Detector 16 Comparator 18 Wafer Sub-Attorney Attorney Atsushi Nakajima Attorney Attorney Kato Kato Attorney Hiroyuki Iida

Front Page Continuation (72) Inventor Ching-Long Cheng United States 12590, Wailingers Falls, New York, Pirain 50 (72) Inventor Mu-Eu Xiao United States 12603, Paquipsi, NY Fairway 7 (72) Inventor James Michael Mulligan USA 12570, Pakuag, NY Box 33, R2 (56) References US Patent 4025442 (US, A)

Claims (9)

[Claims] 1. A method of marking a substrate with a bar code, comprising the step of providing a sequence of marks of substantially uniform width at selectively spaced intervals, said marks having an integer number of spaces between them. A blank spacing is present, the individual blank spacing having a width substantially the same as the width of the uniform width marks, and the sequence of marks also includes a mark and blank spacing having a width of 12 adjacent marks. A method of marking a substrate with a bar code, comprising: a sub-sequence of, wherein the sub-sequence is formed to provide self-clocking information and includes an end mark having a mark next to the blank spacing at its end. 2. The method of claim 1 wherein the marks are spaced between the fixedly spaced subsequence marks to display up to 35 different symbols. 3. The marks are spaced to indicate a plurality of distinct symbols such that the maximum distance between adjacent bars for indicating different symbols is minimized.
A method of marking a substrate with the described bar code. 4. The minimum distance is 5 bars wide.
A method of marking a substrate with the described bar code. 5. A substrate marked according to the method of marking a substrate with a barcode according to claim 1. 6. A substrate having identification information comprising a sequence of marks of substantially uniform width at selectively spaced intervals, the substrate having an integer number of blank intervals between the marks.
The individual blank spacing has a width substantially the same as the width of the uniform width mark, and the sequence of marks also includes a subsequence of marks and blank spacing having a width of 12 adjacent marks. The subsequence is formed to provide self-clocking information and has identification information including blank spacing and endmarks having marks at its ends. 7. The substrate with identification information of claim 6, wherein between the marks of the fixedly separated sub-sequences, the marks are separated to display up to 35 different symbols. 8. A maximum distance between adjacent bars to mark different symbols, wherein the marks are separated to indicate a plurality of distinct symbols between the marks of the fixedly spaced subsequences. The substrate having the identification information according to claim 6, wherein is minimized. 9. The minimum distance is 5 bars wide.
A substrate having the described identification information.